Interactive Bezier curves in VB - vb.net

Question

In preparation for my Fall upcoming Adobe Illustrator class, where students always curse while learning the Pen tool and how to draw Bézier curves, I thought I'd provide them with some "theoretical foundation" outside of Illustrator. So far, I'm able to demonstrate the workings of a curve through four points described by x and y coordinates entered in a separate text boxes (see attached screen capture). My question, how can I "transform" this static demonstration into an interactive one, by allowing the students to "select" control points (shown in blue) and move them around the PictureBox? That's not a simple problem. Any pointers would be appreciated.
Here is my source code so far:
Public Class Form1
Dim Point1_X, Point1_Y, Point2_X, Point2_Y, Point3_X, Point3_Y, Point4_X, Point4_Y As Integer
Dim LignesDeDirection As Boolean
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
LignesDeDirection = False
Point1_X = 100
Point1_Y = 100
Point2_X = 200
Point2_Y = 200
Point3_X = 50
Point3_Y = 250
Point4_X = 400
Point4_Y = 400
tbPoint1_X.Text = Point1_X
tbPoint1_Y.Text = Point1_Y
tbPoint2_X.Text = Point2_X
tbPoint2_Y.Text = Point2_Y
tbPoint3_X.Text = Point3_X
tbPoint3_Y.Text = Point3_Y
tbPoint4_X.Text = Point4_X
tbPoint4_Y.Text = Point4_Y
End Sub
Private Sub PictureBox1_Paint(sender As Object, e As PaintEventArgs) Handles PictureBox1.Paint
e.Graphics.Clear(Color.LightGray)
Dim FondBlanc As New SolidBrush(Color.White)
e.Graphics.FillRectangle(FondBlanc, 0, 0, PictureBox1.Width, PictureBox1.Height)
Dim blackPen = New Pen(Color.FromArgb(128, 128, 128), 1)
Dim blackPen2pix = New Pen(Color.FromArgb(64, 64, 64), 2)
Dim EllipsePen = New Pen(Color.FromArgb(0, 128, 255), 3)
Dim blackPen3 = New Pen(Color.Black, 5.0F)
Dim blackPen2 = New Pen(Color.FromArgb(164, 164, 164), 1)
Dim CouleurPoint As New SolidBrush(Color.Magenta)
Dim CouleurControl As New SolidBrush(Color.Blue)
Dim Color2 = New Pen(Color.FromArgb(128, 128, 128), 1)
Dim PenBleu As New Pen(Color.Black, 2.0F)
PenBleu.EndCap = System.Drawing.Drawing2D.LineCap.Flat 'PenBleu.StartCap = System.Drawing.Drawing2D.LineCap.ArrowAnchor
PenBleu.CustomEndCap = New System.Drawing.Drawing2D.AdjustableArrowCap(8, 8)
Dim point1 As New Point(Point1_X, Point1_Y)
Dim point2 As New Point(Point2_X, Point2_Y)
Dim point3 As New Point(Point3_X, Point3_Y)
Dim point4 As New Point(Point4_X, Point4_Y)
e.Graphics.FillEllipse(CouleurPoint, Point1_X - 5, Point1_Y - 5, 10, 10)
e.Graphics.FillEllipse(CouleurControl, Point2_X - 5, Point2_Y - 5, 10, 10)
e.Graphics.FillEllipse(CouleurControl, Point3_X - 5, Point3_Y - 5, 10, 10)
e.Graphics.FillEllipse(CouleurPoint, Point4_X - 5, Point4_Y - 5, 10, 10)
Dim PenDashMagenta As New Pen(Color.Magenta, 1.5F)
PenDashMagenta.DashStyle = Drawing2D.DashStyle.Dash
Dim PenRéférence As New Pen(Color.ForestGreen, 1.0F)
If cbDirectionLines.Checked = True Then
LignesDeDirection = True
e.Graphics.DrawLine(PenRéférence, Point1_X, Point1_Y, Point2_X, Point2_Y)
e.Graphics.DrawLine(PenRéférence, Point3_X, Point3_Y, Point4_X, Point4_Y)
Else
LignesDeDirection = False
End If
e.Graphics.DrawEllipse(PenDashMagenta, Point1_X - 40, Point1_Y - 40, 80, 80)
e.Graphics.DrawEllipse(PenDashMagenta, Point4_X - 40, Point4_Y - 40, 80, 80)
e.Graphics.DrawBezier(PenBleu, point1, point2, point3, point4)
End Sub
Private Sub btnDisplay_Click(sender As Object, e As EventArgs) Handles btnDisplay.Click
Point1_X = tbPoint1_X.Text
Point1_Y = tbPoint1_Y.Text
Point2_X = tbPoint2_X.Text
Point2_Y = tbPoint2_Y.Text
Point3_X = tbPoint3_X.Text
Point3_Y = tbPoint3_Y.Text
Point4_X = tbPoint4_X.Text
Point4_Y = tbPoint4_Y.Text
PictureBox1.Invalidate()
End Sub
End Class